Blood purine and energy status in rats with colitis

Colitis reduces the blood and tissue levels of adenosine deaminase and adenylate deaminase. Whether this has any effect on blood purines remains to be determined. The aim of this study was to measure the adenylate pool, substrates of the above enzymes, and energy status in blood from rats with colitis. Colitis was induced by intrarectal administration of acetic acid and followed over a period of seven days. The levels of ATP, ADP, AMP, adenosine, inosine, and uric acid were analyzed by HPLC, and energy status was estimated. Myeloperoxidase was used as a marker of colitis. Concentrations of ATP, ADP, AMP and adenosine decreased during days 1-5, whereas energy status decreased on day 2. The concentrations of inosine, uric acid, and hemoglobin remained unaltered, whereas colonic myeloperoxidase activity increased. These, findings demonstrate colitis-induced reduction of the circulating purines, which may be due to their enhanced usage for the repair of the inflamed colon.

Oxidation of pyridine nucleotides during Fas- and ceramide-induced apoptosis in Jurkat cells: correlation with changes in mitochondria, glutathione depletion, intracellular acidification and caspase 3 activation

Jurkat T cells showed a major, early decrease in blue autofluorescence in response to Fas/Apo-1/CD95 cross-linking or stimulation with cell-permeant ceramide. This indicates the oxidation/depletion of NADH or NADPH before the onset of apoptosis. Kinetic studies, cytofluorimetric multiparameter analyses and cell sorting experiments indicated a close temporal relationship between NAD(P)H oxidation/depletion and the dissipation of the mitochondrial transmembrane potential (DeltaPsi(m)). In contrast, NAD(P)H depletion was detected well before several other changes associated with late apoptosis, including enhanced superoxide generation, phosphatidylserine exposure on the cell surface, loss of cytosolic K(+), decreased cytoplasmic pH, nuclear DNA fragmentation, cell shrinkage, loss of viability and the appearance of the mitochondrial antigen APO2.7. Full activation of caspase 9 and caspase 3 appeared to be correlated with the appearance of superoxide anions in the mitochondria, and followed the drop in NADPH. Overexpression of the apoptosis-inhibitory proto-oncogene Bcl-2, which encodes an inhibitor of the mitochondrial permeability transition (PT) pore, delayed both the DeltaPsi(m) disruption and the depletion of NAD(P)H. Similar effects were observed with the pharmacological PT pore inhibitors, bongkrekic acid and cyclosporin A. Thus there appears to be a close functional relationship between mitochondrial and cellular redox changes during early apoptosis; events that are inhibited by Bcl-2.

Hypoxia decreases proteins involved in epithelial electrolyte transport in A549 cells and rat lung

Fluid reabsorption from alveolar space is driven by active Na reabsorption via epithelial Na channels (ENaCs) and Na-K-ATPase. Both are inhibited by hypoxia. Here we tested whether hypoxia decreases Na transport by decreasing the number of copies of transporters in alveolar epithelial cells and in lungs of hypoxic rats. Membrane fractions were prepared from A549 cells exposed to hypoxia (3% O(2)) as well as from whole lung tissue and alveolar type II cells from rats exposed to hypoxia. Transport proteins were measured by Western blot analysis. In A549 cells, alpha(1)- and beta(1)-Na-K-ATPase, Na/K/2Cl cotransport, and ENaC proteins decreased during hypoxia. In whole lung tissue, alpha(1)-Na-K-ATPase and Na/K/2Cl cotransport decreased. alpha- and beta-ENaC mRNAs also decreased in hypoxic lungs. Similar results were seen in alveolar type II cells from hypoxic rats. These results indicate a slow decrease in the amount of Na-transporting proteins in alveolar epithelial cells during exposure to hypoxia that also occurs in vivo in lungs from hypoxic animals. The reduced number of transporters might account for the decreased transport activity and impaired edema clearance in hypoxic lungs.

gamma-glutamyltranspeptidase-deficient knockout mice as a model to study the relationship between glutathione status, mitochondrial function, and cellular function

gamma-Glutamyltranspeptidase (GGT)-deficient mice (GGT(-/-)) display chronic glutathione (GSH) deficiency, growth retardation, and die at a young age (<20 weeks). Using livers from these mice, we investigated the relationship between GSH content, especially mitochondrial, and mitochondrial and cellular function. We found that the GSH content of isolated liver mitochondria was diminished by >/=50% in GGT(-/-) mice when compared with wild-type mice. Respiratory control ratios (RCRs) of GGT(-/-) mice liver mitochondria were </=60% those of wild-type mice primarily as a result of impaired state 3 respiration. Mitochondrial adenine nucleotide content was decreased by >/=40% in mitochondria obtained from GGT(-/-) mice. We observed a strong correlation between mitochondrial GSH content and RCRs. Even moderate decreases (<50%) correlated with adverse effects with respect to respiration. Electron microscopy revealed that livers from GGT(-/-) knockout mice were deprived of fat and glycogen, and swollen mitochondria were observed in animals that were severely deprived of GSH. Thus, GGT(-/-) mice exhibit a loss of GSH homeostasis and impaired oxidative phosphorylation, which may be related to the rate of adenosine triphosphate (ATP) formation and subsequently leads to progressive liver injury, which characterizes the diseased state. We also found that supplementation of GGT(-/-) mice with N-acetylcysteine (NAC) partially restored liver GSH, but fully restored mitochondrial GSH and respiratory function. Electron microscopy revealed that the livers of NAC-supplemented GGT(-/-) mice contained fat and glycogen; however, slightly enlarged mitochondria were found in some livers. NAC supplementation did not have any beneficial effect on the parameters examined in wild-type mice.

Determination of metabolite and regulatory enzyme levels in Dirofilaria immitis and Ascaris suum: a comparative study

Studies on metabolite levels in Dirofilaria immitis revealed similarities in several metabolites with those of Ascaris suum. The glycogen level in the filariid was however 3-4 times lower than that in A. suum. Levels of three regulatory enzymes were also determined in D. immitis and compared with those in A. suum. The activities of Hexokinase and Phosphofructokinase were similar. However, the levels of Glycogen phosphorylase b appeared to be much lower in the filariid than in A. suum. The subtle but important differences observed may reflect modifications of the parasite enzymes suggesting salient differences in the regulation of energy production from carbohydrates in the worms. The differences may also represent specialization required for the unique life style of the worms in their different locations in their hosts.

The role of mitochondrial injury in bromobenzene and furosemide induced hepatotoxicity

Bromobenzene (BB) and furosemide (FS) are two hepatotoxicants whose bioactivation to reactive intermediates is crucial to the development of liver injury. However, the events which lead to hepatocellular toxicity following metabolite formation and covalent binding to cellular macromolecules remain unknown. The present study was undertaken to investigate the effect of administered BB and FS on mitochondrial total glutathione (GSH+GSSG, henceforth referred to as glutathione) content and respiratory function as potential initiating mechanisms of the hepatotoxicity of these compounds in the mouse. Bromobenzene (2 g/kg i.p.) significantly decreased mitochondrial glutathione to 48% of control at 3 h post administration, and to 41% at 4 h. This decrease in mitochondrial glutathione was subsequent to a significant decrease in cytosolic glutathione to 64 and 28% of control at 1 and 2 h, respectively. Oxygen consumption supported by complex I (glutamate-supported) of the respiratory chain was not inhibited by BB until 4 h, where state 3 (active) respiration was reduced to 16% of control. This resulted in a decreased respiratory control ratio (RCR) for complex I-supported respiration. Complex II (succinate)-supported state 3 and state 4 respiration were unaffected by BB until 4 h, at which time they were reduced to 57 and 48% of control, respectively. However, the similar reductions in state 3 and state 4 respiratory rates did not alter the corresponding RCR for complex II. Overt hepatic injury was detected at 4 h, with plasma alanine aminotransferase (ALT) activity increasing significantly at this time point. In contrast to the effects of BB, FS administration (400 mg/kg i.p.) did not alter mitochondrial or cytosolic glutathione, and had no effect on respiration supported by complex I or II for up to 5 h following dosing. However, ALT activity was significantly increased 5 h following FS administration. These results suggest that inhibition of mitochondrial respiratory function coinciding with a decrease in mitochondrial glutathione content may be crucial to the initiation of BB-induced hepatotoxicity, while such events are not required for the initiation of FS-induced hepatotoxicity.

Covalent modification of the catalytic sites of the H+-ATPase from chloroplasts and 2-nitreno-ADP. Modification of the catalytic site 1 (tight) and catalytic sites 1 and 2 together impairs both uni-site and multi-site catalysis of ATP synthesis and ATP hydrolysis

After isolation and purification, the H+-ATPase from chloroplasts, CF0F1, contains one endogenous ADP at a catalytic site, and two endogenous ATP at non-catalytic sites. Incubation with 2-azido-[alpha-32P]ADP leads to tight binding of azidonucleotides. Free nucleotides were removed by three consecutive passages through centrifugation columns, and upon UV-irradiation most of the label was covalently bound. The labelled enzyme was digested by trypsin, the peptides were separated by ion exchange chromatography into nitreno-AMP, nitreno-ADP and nitreno-ATP labelled peptides, and these were then separated by reversed phase chromatography. Amino acid sequence analysis was used to identify the type of the nucleotide binding site. After incubation with 2-azido-[alpha-32P]ADP, the covalently bound label was found exclusively at beta-Tyr-362. Incubation conditions with 2-azido-[alpha-32P]ADP were varied, and conditions were found which allow selective binding of the label to different catalytic sites, designated as 1, 2 and 3 in order of decreasing affinity for ADP, and either catalytic site 1 or catalytic sites 1 and 2 together were labelled. For measurements of the degree of inhibition by covalent modification, CF0F1 was reconstituted into phosphatidylcholine liposomes, and the membranes were energised by an acid-base transition in the presence of a K+/valinomycin diffusion potential. The rate of ATP synthesis was 50-80 s(-1), and the rate of ATP hydrolysis was 15 s(-1) measured under multi-site conditions. Covalent modification of either catalytic site 1 or catalytic sites 1 and 2 together inhibited ATP synthesis and ATP hydrolysis equally, the degree of inhibition being proportional to the degree of modification. Extrapolation to complete inhibition indicates that derivatisation of catalytic site 1 leads to complete inhibition when 1 mol 2-nitreno-ADP is bound per mol CF0F1. Derivatisation of catalytic sites 1 and 2 together extrapolates to complete inhibition when 2 mol 2-nitreno-ADP are bound per CF0F1. The rate of ATP synthesis and the rate of ATP hydrolysis were measured as a function of the substrate concentration from multi-site to uni-site conditions with derivatised CF0F1 and with non-derivatised CF0F1. ATP synthesis and ATP hydrolysis under uni-site and under multi-site condition were inhibited by covalent modification of either catalytic site 1 or catalytic sites 1 and 2 together. The results indicate that derivatisation of site 1 inhibits activation of the enzyme and that cooperative interactions occur at least between the catalytic sites 2 and 3.

Increase in vulnerability of middle-aged rat brain to lead by cerebral energy depletion

The neurotoxic effects of low-level lead (Pb) during senescence are increasing interests of importance. We investigated the effects of low-level Pb on the brain in a normal condition and a pathophysiological condition of energy shortage that is commonly found in age-related neurological diseases. Middle-aged rats (15 months old) were exposed to 200 mg/l Pb acetate in drinking water for 2 months and thereafter received bilateral intracerebroventricular injections of streptozotocin (STZ). After 1 month's additional exposure to the same level of Pb solution as before the rats were sacrificed. Blood and brain Pb levels were measured by graphite furnace atomic absorption spectrophotometry. Energy-rich phosphate levels in the brain were determined by high-performance liquid chromatography equipped with a UV detector. Astroglial activation and glucose-regulated protein (GRP)94 expression were examined immunohistochemically. Exposure to Pb increased the blood Pb level to 10.8 microg/dl and the brain Pb level to 0.052 microg/g. But a significant additional increase in the brain Pb level, to 0.101 microg/g, became obvious in rats treated with Pb + STZ. Both Pb and STZ induced perturbation in brain energy metabolism, but no further alteration in energy metabolite levels was found in rats treated with Pb + STZ. Astroglial activation and GRP94-positive astrocytes and neurons were found only in the brains of Pb + STZ-treated rats. These results suggest that exposure to low-level Pb can perturb brain energy metabolism and the brain becomes more vulnerable to Pb when it is under energy stress.

Assay of ATPase and Na,K-ATPase activity using high-performance liquid chromatographic determination of ADP derived from ATP

An HPLC assay for determination of ATPase activity was developed and validated. After stopping the enzyme reaction of the enzyme source (rat renal cortical basolateral membranes) with ATP, products derived from ATP were analyzed by two methods; HPLC determination of ADP derived from ATP, and colorimetry of inorganic phosphorus (Pi) released from ATP. This HPLC procedure was precise and linear over the range of protein amount of the enzyme source studied, and the intra-and inter-assay variations were lower than 10%. The values that were obtained by the two methods revealed a significant correlation. Also, even when the samples contained Pi or were contaminated with Pi, this HPLC method allowed determination of ATPase activity. In addition, when ouabain was used as an inhibitor, the HPLC method was found to be applicable for Na,K-ATPase determination. This indicated that this HPLC assay would enable determination of ATPases other than Na,K-ATPase, when other inhibitors are employed instead of ouabain.

Measurement of the ADP:ATP ratio in human leukaemic cell lines can be used as an indicator of cell viability, necrosis and apoptosis

In this study the relative levels of ADP and ATP have been measured in cells undergoing apoptosis. Using HL60, CEM7, Jurkat and U937 cell lines and cytotoxic agents known to induce apoptosis, there was a significant correlation (P<0.01 for all models) between the ADP:ATP ratio and the degree of apoptosis measured by TUNEL and estimation of the sub G(0) fraction by propidium iodide staining and flow cytometry. The ratio measured in viable proliferating cells was found to be less than 0.11 compared with ratios between 0.11 and 1.0 seen in cells undergoing apoptosis. The higher the percentage of hypodiploidy the greater the ratio. Necrosis induced by heat shock resulted in ADP:ATP ratios in excess of 15.0. When primary cultures of AML blast cells were used, there was again a significant correlation between the ADP:ATP ratio and the degree of hypodiploidy. Recent evidence suggests that apoptosis is accompanied by opening of the mitochondrial permeability pores, leading to disruption of the mitochondrial transmembrane potential (DeltaPsi(m)). This results in caspase activation due to the release of cytochrome c and apoptogenic factors into the cytosol. In five experiments using CEM7 and dexamethasone the mitochondrial transmembrane potential was assessed using the fluorescent cyanine dye JC-1 and flow cytometry. Functioning mitochondria concentrate the JC-1 to produce red fluorescence. Loss of mitochondrial transmembrane potential results in green fluorescence only. The percentage of cells exhibiting red fluorescence correlated positively with the ATP values and negatively with the ADP:ATP ratio.

Regulation of the actin cycle in vivo by actin filament severing

Cycling of actin subunits between monomeric and filamentous phases is essential for cell crawling behavior. We investigated actin filament turnover rates, length, number, barbed end exposure, and binding of cofilin in bovine arterial endothelial cells moving at different speeds depending on their position in a confluent monolayer. Fast-translocating cells near the wound edge have short filament lifetimes compared with turnover values that proportionately increase in slower moving cells situated at increasing distances from the wound border. Contrasted with slow cells exhibiting slow actin filament turnover speeds, fast cells have less polymerized actin, shorter actin filaments, more free barbed ends, and less actin-associated cofilin. Cultured primary fibroblasts manifest identical relationships between speed and actin turnover as the endothelial cells, and fast fibroblasts expressing gelsolin have higher actin turnover rates than slow fibroblasts that lack this actin-severing protein. These results implicate actin filament severing as an important control mechanism for actin cycling in cells.

Alkanols inhibit respiration of intact mitochondria and display cutoff similar to that measured in vivo

Primary aliphatic alcohols from hexanol to pentadecanol were tested for their effects on the succinate-supported respiration of intact mitochondria isolated from rat liver. Alkanols were found to inhibit State 3 and uncoupled respiration. The ADP/oxygen ratios, a measure of the efficiency of oxidative phosphorylation, also were lowered, but to a lesser degree when compared on the basis of percentage of controls. Given each alkanol's nearly identical effect on State 3 and uncoupled respiration, action is not directly on ATP synthase, but earlier in the respiratory process. In agreement with many other studies of the homologous series of alkanols, potency increased with number of carbons in the chain until reaching a peak, in this case at undecanol, then tapered off to tridecanol before reaching a cutoff, at tetradecanol. If tetradecanol or longer homologs have activity, it is only after a lag phase of >15-min preincubation. All alkanols up to tridecanol also acted as uncouplers. At higher doses, hexanol inhibited State 4 rates, whereas longer chain alkanols did not, even at doses that completely eliminated respiratory control. Hexanol and decanol also were assayed against freeze-thawed (broken) mitochondria to distinguish effects on the mitochondrial substrate carrier from those on the electron transport chain. Both compounds were only weak inhibitors of respiration in broken mitochondria, suggesting that inhibition originates from interference with the dicarboxylate carrier, which must transport succinate across the mitochondrial membranes before it can be fed into complex II, rather than affecting the electron transport chain itself.

Reperfusion lung injury after cold preservation correlates with decreased levels of intrapulmonary high-energy phosphates

BACKGROUND

To evaluate the role of energy state in primary graft dysfunction, which is crucial in lung transplantation, we investigated the relationship between intrapulmonary high-energy phosphate compounds and reperfusion lung injury after cold preservation.

METHODS

Using an isolated rat lung perfusion model with fresh rat blood as perfusate, rat lungs were exposed to various cold preservation periods (0, 6, 9, and 12 hr) and reperfused.

RESULTS

We found that extending the preservation period exacerbated the pulmonary hemodynamics after reperfusion. The levels of intrapulmonary high-energy phosphate compounds did not change during cold preservation, but these levels after reperfusion decreased as the preservation period was prolonged. The pulmonary hemodynamics after reperfusion were inversely correlated with the intrapulmonary high-energy phosphate compound levels after reperfusion. Total adenine nucleotide and ATP were sensitive indicators of reperfusion lung injury after cold preservation. Energy charge was not a sensitive indicator. The decreased levels of intrapulmonary high-energy phosphate compounds after reperfusion following cold preservation period were partially caused by their decreased production.

CONCLUSIONS

These results demonstrated that reperfusion lung injury after cold preservation was closely correlated with decreased levels of intrapulmonary high-energy phosphate compounds after reperfusion, although the levels of the intrapulmonary high-energy phosphate compounds did not change during cold preservation of up to 12 hr.

Coordinated changes of adenylate energy charge and ATP/ADP: use in ecotoxicological studies

The coordinated variations of the adenylate energy charge and ATP/ADP ratio were modeled and a function that depends on the numerical value of the adenylate kinase-catalyzed reaction has been derived. The model allows sensitive detection of the effects of xenobiotics on adenylate kinase and its cellular environment and offers a robust estimation of the direct or indirect effects of pollutants on the adenylate kinase system: data obtained in laboratory studies on shrimp exposed to cadmium and in field studies on oysters either exposed to polychloro-biphenyl compounds or located in a heavily polluted area indicate that xenobiotics affect the adenylate kinase reaction directly or by changing its cellular environment. These results demonstrate that application of the model to the treatment of ecotoxicological data allows detection of energetic changes that would have been missed by simple analysis of the usual energetic parameters, and should overcome problems encountered in using energetic parameters during assessment of pollution monitoring.

Permanent cerebral hypoperfusion: 'preconditioning-like' effects on rat energy metabolism towards acute systemic hypotension

Chronic cerebrovascular disorders are often complicated by additional temporary ischaemic insults, resulting in substantial deterioration of brain energy metabolism. In the present study, chronic limitations of oxygen supply were induced in Wistar rats by 2 weeks of permanent bilateral common carotid artery occlusion (2-vo) to initiate a 'preconditioning-like' effect that protects rat brain energy metabolism against further acute systemic hypotension (15 min). Haemodynamic parameters, arterial blood gases and body temperature were monitored. Energy metabolites were determined in rat parietotemporal cerebral cortex: adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP), phosphocreatine (PCr), and adenosine by the high-pressure liquid chromatography (HPLC) technique and lactate spectrophotometrically. After 2 weeks, permanent 2-vo led to a significant decrease in the concentrations of cortical tissue ATP and PCr, from 3.06+/-0.48 to 2. 09+/-0.28 and from 4.27+/-0.63 to 3.35+/-0.41 micromol/g, respectively. These changes were associated with a two-fold increase in AMP and adenosine. Acute systemic hypotension alone (non-preconditioning) reduced ATP and PCr drastically, to 0.97+/-0. 51 and 1.76+/-1.23 micromol/g. Tissue concentrations of lactate, AMP, and adenosine were markedly increased, three- to five-fold, in 'non-preconditioned' brain tissue. In contrast, after 2 weeks of 2-vo acute hypotension did not significantly alter the cortical energy state any further. The effects of preconditioning on tissue ATP and PCr were most pronounced at 5 min and 48 h after reperfusion. In conclusion, permanent 2-vo seems to activate compensatory mechanisms, which effectively protect the rat's cortical energy metabolism against an additional ischaemic attack ('preconditioning-like' effect).

31P magnetic resonance spectroscopy study of phosphocreatine recovery kinetics in skeletal muscle: the issue of intersubject variability

We have analyzed by (31)P MRS the relationship between kinetic parameters of phosphocreatine (PCr) recovery and end-of-exercise status under conditions of moderate and large acidosis induced by dynamic exercise. Thirteen healthy subjects performed muscular contractions at 0.47 Hz (low frequency, moderate exercise) and 0.85 Hz (high frequency, heavy exercise). The rate constant of PCr resynthesis (k(PCr)) varied greatly among subjects (variation coefficients: 43 vs. 57% for LF vs. HF exercises) and protocols (k(PCr) values: 1.3+/-0.5 min(-1) vs. 0.9+/-0.5 min(-1) for LF vs. HF exercises, P<0.03). The large intersubject variability can be captured into a linear relationship between k(PCr), the amount of PCr consumed ([PCr(2)]) and pH reached at the end of exercise (pH(end)) (k(PCr)=-3.3+0.7 pH(end)-0.03 [PCr(2)]; P=0.0007; r=0.61). This dual relationship illustrates that mitochondrial activity is affected by end-of-exercise metabolic status and allows reliable comparisons between control, diseased and trained muscles. In contrast to k(PCr), the initial rate of PCr recovery and the maximum oxidative capacity were always constant whatever the metabolic conditions of end-of-exercise and can then be additionally used in the identification of dysfunctions in the oxidative metabolic pathway.

Analysis of sugar metabolism in an EPS producing Lactococcus lactis by 31P NMR

Sugar metabolism and exopolysaccharide (EPS) production was analysed in Lactococcus lactis by in vivo 31P NMR. Transient production of several sugar phosphates, transient depletion of intracellular phosphate, transient production of ATP and UTP, transient acidification of the medium and alkalinisation of the cytoplasm could be observed in a period of 20 min upon energization by the addition of glucose. EPS and non-EPS producing variants showed similar NMR spectra, the exception being two pH-dependent resonances observed in the former. They were already observed before addition of glucose and their response to glucose incubation reflected exposure to the medium. They are presumably phosphorylated poly- or oligosaccharides being loosely adhered to cell walls. By freezing and perchloric acid extraction of the cell material, different types of phosphorylated compounds could be recognised in the NMR spectra such as fructose-1-6-diphosphate, nucleotides (like ADP, ATP, UTP and TDP) and several nucleotide sugars. The ongoing work is focused on identifying the unknown peaks and quantifying the differences between wild-type cells and the EPS producing variant.

Endothelin-1 in the brain of patients with galactosialidosis: its abnormal increase and distribution pattern

Endothelin-1 is a peptidic substrate in vitro of lysosomal protective protein/cathepsin A (PPCA) with serine carboxypeptidase activity. Endothelin-1-specific immunoreactivity has been demonstrated to be markedly increased and distributed abnormally in the neurons and glial cells within autopsied brain regions, including the cerebellum, hippocampal formation, and spinal cord, of patients affected with galactosialidosis, a human PPCA deficiency. The genetic defect of the endothelin-1 degrading activity of PPCA is suggested to cause some of the neurological abnormalities of this disease.

31P MRS measurement of mitochondrial function in skeletal muscle: reliability, force-level sensitivity and relation to whole body maximal oxygen uptake

The reliability, relation to whole-body maximal oxygen uptake (VO(2max)), and force-level sensitivity of (31)P MRS markers of mitochondrial function were studied in 39 normal-weight women. Following 90 s isometric plantar-flexion exercises at 45, 70 and 100% of maximum voluntary contraction, skeletal muscle mitochondrial function was determined from the phosphocreatine recovery time constant (TC(PCr)), the ADP recovery time constant (TC(ADP)), and the rate of change in PCr during the first 14 s of recovery (OxPhos). VO(2max) was measured on a treadmill. Test-retest measurements were obtained in a subset of seven women. Overall, TC(PCr), TC(ADP) and OxPhos were reproducible for all exercises (coefficients of variation = 2.3-19.3%). With increasing force-level, TC(PCr) was prolonged (29.0 +/- 8.2, 31.9 +/- 9.0 and 35.4 +/- 9.5 s), OxPhos was increased (0.159 +/- 0.081, 0.247 +/- 0.090 and 0.310 +/- 0.114), and TC(ADP) was shortened (22.4 +/- 7.9, 21.3 +/- 6.2, and 19.5 +/- 6.7; p < 0.01). All MRS markers of mitochondrial function were correlated with VO(2max) (r = 0.41-0.72; p < 0.05). These results suggest that measurements of TC(PCr), TC(ADP) and OxPhos yield reproducible results that correlate with whole-body VO(2max) and that vary in force-level sensitivity.

Heart preservation in HTK solution: role of coronary vasculature in recovery of cardiac function

BACKGROUND

Poor myocardial tolerance to prolonged cold ischemia remains a major concern in heart transplantation. In this study, we estimated superiority of Histidine-Tryptophan-Ketoglutarate (HTK) over University of Wisconsin (UW) as a cardiac preservation solution.

METHODS

Isolated rat hearts were mounted on a Langendorff apparatus to estimate the baseline cardiac function. The hearts were arrested and stored at 4 degrees C in UW and HTK solution for 8 hours, and then reperfused. The aortic flow, coronary flow, cardiac output, rate pressure product, and left ventricular dp/dt in the HTK group recovered significantly more than the UW group. The values of myocardial total adenine nucleotides and the adenosine triphosphate to adenosine diphosphate ratio were higher in the HTK than in the UW group. We also examined coronary vascular responsiveness using left coronary arteries dissected from the rat hearts before flushing, before storage, after storage, and after reperfusion.

RESULTS

The maximal relaxation response to acetylcholine was significantly higher in the HTK than in the UW group after reperfusion, although there were no significant differences at each stage before reperfusion. In addition, the endothelium-independent relaxation response to sodium nitroprusside in the HTK group was also well preserved after reperfusion.

CONCLUSIONS

These results indicate that HTK is superior to UW solution for cardiac preservation. HTK protects coronary vasculature during preservation, which together with reperfusion might lead to improved functional cardiac recovery following preservation.

Luminometric assays of ATP, phosphocreatine, and creatine for estimation of free ADP and free AMP

We present methods to measure ATP, phosphocreatine, and total creatine (the sum of creatine and phosphocreatine) in alkaline cell extracts. Knowledge of these parameters, together with the known equilibrium constants for the creatine kinase and adenylate kinase-catalyzed reactions, allows one to estimate the levels of free ADP and free AMP inside cells. The enzymatic assays for the above-mentioned metabolites all lead up to the production of ATP, which is measured luminometrically with the ATP-dependent oxidation of luciferin catalyzed by firefly luciferase. To determine phosphocreatine, endogenous ATP is first destroyed, and phosphocreatine is then quantitatively reacted with exogenous ADP to form ATP. Total creatine is measured after quantitative conversion of creatine to phosphocreatine with a large excess of exogenous ATP, conversion of all ATP to ADP, and final reaction of phosphocreatine with ADP to form ATP. We used 5-microl samples in 0.5-ml microcentrifuge tubes and subsequent 5-microl additions of analytical reagents. We expect that the volumes can be changed easily. We tested the methods with glucagon- and insulin-secreting cells. Estimates of free ADP and AMP are expected to be useful in many different areas of research, such as cellular energy metabolism, purine nucleotide metabolism, adenine nucleotide gating of ion channels, and release of vasoactive or angiogenic factors.

Effect of adenine nucleotide pool size in mitochondria on intramitochondrial ATP levels

Net adenine nucleotide transport into and out of the mitochondrial matrix via the ATP-Mg/Pi carrier is activated by micromolar calcium concentrations in rat liver mitochondria. The purpose of this study was to induce net adenine nucleotide transport by varying the substrate supply and/or extramitochondrial ATP consumption in order to evaluate the effect of the mitochondrial adenine nucleotide pool size on intramitochondrial adenine nucleotide patterns under phosphorylating conditions. Above 12 nmol/mg protein, intramitochondrial ATP/ADP increased with an increase in the mitochondrial adenine nucleotide pool. The relationship between the rate of respiration and the mitochondrial ADP concentration did not depend on the mitochondrial adenine nucleotide pool size up to 9 nmol ADP/mg mitochondrial protein. The results are compatible with the notion that net uptake of adenine nucleotides at low energy states supports intramitochondrial ATP consuming processes and energized mitochondria may lose adenine nucleotides. The decrease of the mitochondrial adenine nucleotide content below 9 nmol/mg protein inhibits oxidative phosphorylation. In particular, this could be the case within the postischemic phase which is characterized by low cytosolic adenine nucleotide concentrations and energized mitochondria.

Effects of noradrenaline, the calcium ionophore A23187, forskolin, sodium nitroprusside and glibenclamide on the degradation of extracellular adenosine 5'-triphosphate by the rat isolated vas deferens

1. The effects of noradrenaline (NA), the calcium ionophore A23187, forskolin, sodium nitroprusside (SNP) and the K+-channel blocker glibenclamide on the degradation by ectonucleotidases of extracellular adenosine 5'-triphosphate (ATP) were studied in the rat vas deferens. 2. ATP (100 microM) was rapidly broken down by the rat vas deferens with a half-life of 5.83 +/- 0.40 min via adenosine 5'-diphosphate (ADP) and adenosine 5'-monophosphate (AMP), with the final degradation product being inosine and with little adenosine being detected in the samples. 3. Preincubation for 1 h with NA (10 microM), A23187 (10 microM), or glibenclamide (100 microM) had no significant effect on the breakdown of ATP or the production of metabolites. However, both forskolin (10 microM) and SNP (1 microM) significantly increased the concentrations of AMP detected with time. In the case of SNP (1 microM) there was also a significant reduction in the rate of production of inosine, while in the case of forskolin (10 microM) there was a significant increase in the rate of removal of ATP. 4. These results suggest that preincubation with SNP may inhibit 5'-nucleotidase and so reduce the metabolism of AMP, while preincubation with forskolin may increase the activity of the ectonucleotidases responsible for production of AMP from ATP.

In vivo determination of altered hemoglobin saturation in dogs with M-type phosphofructokinase deficiency

Muscle-type phosphofructokinase (M-PFK) deficiency causes an exertional myopathy and chronic hemolysis in affected humans and dogs, the only animal model available. Deficient individuals have impaired glycolytic metabolism, impaired oxidative metabolism, and increased hemoglobin-oxygen (HbO2) affinity as a result of low 2,3-diphosphoglycerate (2,3-DPG) levels. The purpose of this study was to determine if PFK-deficient muscle has abnormal oxygen saturation during exercise. Oxygen saturation of hemoglobin/myoglobin was measured noninvasively in skeletal muscle during progressive muscle activation using near-infrared spectroscopy (NIRS). Muscle metabolites were also measured using magnetic resonance spectroscopy (MRS). PFK-deficient and normal dogs were anesthetized and the cranial tibial muscles stimulated for 6 min at each of four different rates (1, 2, 4, and 8 Hz). With increasing stimulation, muscles from normal dogs showed progressive decrease in hemoglobin saturation. In contrast, PFK-deficient dogs exhibited either an increase in hemoglobin saturation or an initial decrease with no further change. PFK-deficient muscles accumulated 11.1 +/- 3.5 mmol/L of sugar phosphate which was not seen in normal muscle and had higher calculated [ADP] levels at each stimulation level, indicating impaired oxidative metabolism. These findings are consistent with the hypothesis that these animals have impaired oxidative metabolism and impaired muscle O2 extraction from hemoglobin due to increased HbO2 affinity. NIRS appears to be a useful noninvasive method of monitoring tissue oxygen saturation in normal or disease conditions.

Rapid purification of membrane extrinsic F1-domain of chloroplast ATP synthase in monodisperse form suitable for 3D-crystallization

A new chromatographic procedure for purification of the membrane extrinsic F1-domain of chloroplast ATP synthase is presented. The purification is achieved by a single anion exchange chromatography step. Determination of the enzyme-bound nucleotides reveals only 1 mole of ADP per complex. The purified enzyme shows a latent Ca(2+)-dependent ATPase activity of 1.0 mumol.mg-1 min-1 and a Mg(2+)-dependent activity of 4.4 mumol.mg-1 .min-1. Both activities are increased up to 8-10-fold after dithiothreitol activation. Analysis of the purified F1-complex by SDS/PAGE, silver staining and immunoblotting revealed that the preparation is uncontaminated by fragmented subunits or ribulose-1,5-bisphosphate carboxylase/oxygenase. Gel filtration experiments indicate that the preparation is homogenous and monodisperse. In order to determine the solubility minimum of the purified F1-complex the isoelectric point of the preparation was calculated from pH mapping on ion exchange columns. In agreement with calculations based on the amino acid sequence, a slightly acidic pI of 5.7 was found. Using ammonium sulphate as a precipitant the purified CF1-complex could be crystallized by MicroBatch.

Evidence of mitochondrial dysfunction in broilers with pulmonary hypertension syndrome (Ascites): effect of t-butyl hydroperoxide on hepatic mitochondrial function, glutathione, and related thiols

The purpose of this study was to assess mitochondrial function and glutathione (a mitochondrial antioxidant) in response to oxidative stress in mitochondria in vitro obtained from broilers with and without pulmonary hypertension syndrome (PHS). Liver mitochondria from Control and PHS broilers were incubated with 0, 1, and 5-mM tertiary-butyl hydroperoxide (tBH). Indices of mitochondrial function [the respiratory control ratio (RCR) and the adenosine diphosphate to oxygen ratio (ADP:O)], and levels of mitochondrial and extra-mitochondrial reduced (GSH) and oxidized (GSSG) glutathione, cysteine, cystine, glutamate and cysteinyl-glycine were determined following tBH treatment. Lower RCR and ADP:O values were observed in PHS mitochondria than in controls. Whereas control mitochondria remained coupled (RCR > 2.0), only 3 PHS preparations remained coupled after 60 min of incubation with 5 mM tBH, indicating a greater susceptibility to oxidative stress in PHS mitochondria. The lower RCR in PHS mitochondria was due to increased oxygen consumption during State IV respiration. Oxidative stress following tBH treatment (decreased GSH and increased GSSG) was observed, but there were no differences in GSH or GSSG between control and PHS mitochondria. The PHS mitochondria did exhibit elevated mitochondrial and extramitochondrial cystine than controls, however. The results indicate that PHS mitochondria do not lack antioxidant protection from GSH, but lower RCR and ADP:O ratios in PHS mitochondria indicate a dysfunction that may contribute to the pathophysiology of this metabolic disease in broilers.

Serial experimental and clinical studies on the pathogenesis of multiple organ dysfunction syndrome (MODS) in severe burns

These serial clinical and experimental studies were designed to clarify the pathogenesis of postburn MODS. Both animal and clinical studies were performed. In animal experiments, 46 male cross-bred dogs were cannulated with Swan-Ganz catheters and 39 of them were inflicted with 50% TBSA third degree burns (7 were used as controls). The burned dogs were randomly divided into 4 groups: immediate infusion, delayed infusion, delayed fast infusion and delayed fast infusion combined with ginsenosides. All dogs were kept under constant barbiturate sedation during the whole study period. Hemodynamics, visceral MDA, mitochondrial respiratory control rate (RCR) and ADP/O ratio, ATP, succinic dehydrogenase (SDH), organ water content as well as light and electron microscopy of visceral tissues were determined. In the clinical study, 61 patients with extensive deep burns were chosen, of which 16 sustained MODS. Plasma TXB2/6-keto-PGF1alpha ratio, TNF, SOD, MDA, circulatory platelet aggregate ratio (CPAR), PGE2, interleukin-1, total organ water content and pathological observations of visceral tissues from patients who died of MODS were carried out. Results demonstrated that ischemic-reperfusion damage due to severe shock, sepsis and inhalation injury are three main causes of postburn death. All inflammatory mediators increased markedly in both animals and patients who sustained organ damage or MODS. SDH, RCR, ADP/O and ATP decreased significantly. These findings suggested that ischemic damage and systemic inflammatory response syndrome (SIRS) initiated by mediators or cytokines might be important in the pathogenesis of postburn MODS.

Protein cross talking through osmotic work: the free energy of formation of the MgADP-myosin complexes at the muscle protein osmotic pressure

A method is presented to determine the energy of formation of the myosin-ADP complexes at the muscle protein osmotic pressure. It is found that, at 18 kP, the putative protein osmotic pressure in skeletal muscle, the increase of MgADP from 0.05 to 2 mmolal, increases the free energy of myosin-ADP and of myosin-(ADP)2 by 0. 756 and by 9.85 kJ/mol, respectively, and decreases the free energy of myosin by 8.34 kJ erg/mol. It is pointed out that the local changes of water chemical potential, induced by the binding of MgADP to myosin, can be sensed by other structures of the contractile machinery, which per se may even be insensitive to MgADP. Cross talking between macromolecules can thus be achieved by changes of the water chemical potential.

Occurrence of prostasome-like membrane vesicles in equine seminal plasma

Equine seminal plasma was shown to contain membrane vesicles that are similar to the well characterized prostasomes in human seminal plasma. Determination of nucleoside and nucleotide concentrations of these particles have shown that ATP, ADP and adenosine are the main components of the nucleotidic pool. 5' nucleotidase, endopeptidase and dipeptidyl peptidase i.v. activities have been found on the surface of the particles. The interaction between these prostasome-like vesicles and spermatozoa was demonstrated by electron micrograph scans which revealed the steps of a fusion-like process leading to mixing of the membranes. In addition, endopeptidase activity, a marker enzyme of these seminal vesicles that is normally absent from equine spermatozoa, was shown to be acquired by these cells after interaction with the vesicles. The addition of these vesicles to equine spermatozoa resulted in the modification of adenylate catabolism. Therefore, a role in stabilizing the energy charge of the spermatozoa thus allowing longer viability is proposed for these organelles.

Muscle anaerobic response to a maximal treadmill exercise test in Standardbred trotters

The purpose of this study was to develop a standardised maximal treadmill exercise test performed until fatigue in order to find reproducible markers for anaerobic metabolism, specifically adenine nucleotide degradation. Six Standardbred trotters performed an incremental maximal treadmill exercise test in 1 min steps (starting with 7 m/s) until they could no longer keep pace with the treadmill. The test was performed twice with at least one week between the tests. Heart rate was recorded and venous blood samples were obtained during the test and in the recovery period for determination of plasma lactate, hypoxanthine, xanthine and uric acid. Muscle biopsy samples (m. gluteus) were collected at rest, immediately post exercise, and after 15 min recovery and analysed for their concentrations of glycogen, creatine phosphate (CP), adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP) and muscle lactate (MLa). Significant decreases in glycogen, CP and ATP and significant increases in IMP and MLa were seen immediately post exercise. None of these metabolites had returned to resting levels after 15 min of recovery. A marked increase in plasma lactate (PLa) occurred during exercise and the peak concentration (mean value = 27.2 mmol/l) was reached within 5 min of recovery. Plasma uric acid concentration did not increase during exercise but rose markedly immediately post exercise, reaching the highest level (mean value = 121.5 micromol/l) at 20-30 min recovery. The duration of the maximal test was related to peak PLa and the uric acid concentration at 30 min of recovery. A correlation was also found between the ATP and IMP concentrations immediately post exercise and the plasma uric acid concentration at 30 min of recovery. The results show that this treadmill test triggered anaerobic metabolism and also that uric acid concentration post exercise seems to be a marker for the adenine nucleotide degradation that occurs during intense exercise. No significant differences were seen in metabolic response between the 2 test occasions.

Colorimetric determination of the purity of 3'-phospho adenosine 5'-phosphosulfate and natural abundance of 3'-phospho adenosine 5'-phosphate at picomole quantities

This work presents novel colorimetric methods not only to measure 3'-phospho adenosine 5'-phosphate (PAP) and 3'-phospho adenosine 5'-phosphosulfate (PAPS) in the range of picomoles, but also to determine the purity of PAPS or PAP contaminants in PAPS in the range of nanomoles. These methods exploit the availability of overexpressed phenol sulfotransferase (PST) and the fact that sulfuryl group transfer requires the use of PAP or PAPS as a cofactor or cosubstrate. Experimental results indicate that absorption at 400 nm due to the production of 4-nitrophenol (pNP) is catalyzed by PST when the sulfuryl group transfers from 4-nitrophenylsulfate (pNPS) to PAP or to 2-napthol. In the absence of an acceptor substrate, PAPS is hydrolyzed to PAP by PST and is determined by sulfation with pNPS before and after this reaction. The change of absorption of pNP at 400 nm corresponds to the amount of PAP that is hydrolyzed from PAPS. Moreover, a standard curve is constructed using authentic PAP and PAP-free PST. Furthermore, this curve is used to determine the amount of PAP in extracts of pig liver, rat liver, and Escherichia coli.

Influence of vitamin E succinate on retinal cell survival

In this study, we analyzed the influence of vitamin E succinate (5-80 microM), supplemented in the culture medium, on the survival of cultured retinal cells. The release of lactate dehydrogenase (LDH) was decreased in the presence of low concentrations (10-20 microM) of vitamin E succinate, whereas high concentrations (80 microM) induced a significant increase (about 2-fold) in the release of LDH, indicating a reduction of plasma membrane integrity. Supplementing with vitamin E succinate (80 microM) greatly enhanced its cellular content, as compared to vitamin E acetate (80 microM), and the membrane order of the retinal cells, as evaluated by the fluorescence anisotropy (r) of TMA-DPH (1-(4-(trimethylammonium)-phenyl)-6-phenylhexa-1,3,5-triene), was not altered. Furthermore, vitamin E succinate was more potent than vitamin E acetate in reducing thiobarbituric acid reactive substances (TBARS) formation upon ascorbate-Fe2+-induced oxidative stress (TBARS formation after cell oxidation decreased by about 15-fold or 1.6 fold, respectively, in the presence of 20 microM vitamin E succinate or 20 microM vitamin E acetate). A decrease in MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) reduction induced by supplementing with vitamin E succinate (80 microM), to 35.99 +/- 1.96% as compared to the control, but not by vitamin E acetate (80 microM), suggests that vitamin E succinate may affect the mitochondrial activity. Vitamin E succinate also reduced significantly the ATP:ADP ratio in a dose-dependent manner, indicating that vitamin E succinate-mediated cytotoxic effects involve a decrement of mitochondrial function.

Changes in the proton potential and the cellular energetics of Escherichia coli during growth by aerobic and anaerobic respiration or by fermentation

The energetic parameters of Escherichia coli were analyzed for the aerobic/anaerobic transition. The electrochemical proton potential (delta p) across the cytoplasmic membrane was determined in the steady state of respiration with O2, nitrate, fumarate, dimethylsulfoxide (Me2SO), and for fermentation. With O2, a proton potential of -160 mV was obtained. For anaerobic respiration with nitrate, fumarate or Me2SO, delta p decreased only slightly by about 20 mV in contrast to earlier assumptions, whereas delta p dropped by approximately 40 mV during fermentation. Under all conditions, the membrane potential (delta psi) contributed the major portion to delta p. The cellular ATP levels were highest for aerobic growth (about 13 micromol/g dry cells) and decreased to 3-6 micromol/g in anaerobic metabolism. Delta G'Phos, however, was constant due to equivalent changes of the ADP contents. Transition to the stationary growth phase caused a massive drop in the ATP content. It is concluded that, during anaerobic respiration, the energetic situation for the bacteria is very similar to that for aerobic growth with respect to delta G'Phos and delta p whereas, for fermentation, a significant decrease in delta p was observed. The consequences for the cellular energetics and for the regulation of the aerobic/anaerobic transition are discussed.

Biochemical changes in denervated muscle identified by magnetic resonance spectroscopy

OBJECTIVE

Magnetic resonance spectroscopy (MRS) has the potential to noninvasively delineate early biochemical changes in denervated muscle. In this study, we examine metabolic changes in denervated rat facial muscles using quantitative invitro 1H and 31P MRS.

METHODS

Forty male Wistar rats were subjected to transection of the facial nerve trunk on the left and sham exposure on the right, and allowed to recover. The animals were then reoperated at 1, 2, 4, or 8 weeks after the initial procedure. EMG of the facial muscles and facial nerve conduction studies were performed at both time points, and facial muscles were harvested from normal and control sides at the second procedure. Perchloric acid extracts of facial muscles were then prepared for analysis using MRS.

RESULTS

The results showed a progressive time-dependent decrease in Cr, PCr, Pi, ATP, and ADP all on the transected side.

CONCLUSION

This study is an important step in the development of clinically relevant noninvasive methods of assessing and quantifying degeneration in nerve-muscle systems.

Detection of early ischemic damage by analysis of mitochondrial function in skinned fibers

The skinned fibers technique was applied for studies of the effects of global acute ischemia (1 h at 37 degrees C) and long time (15 h) hypothermic (4 degrees C) preservation of isolated rat hearts under different conditions (immersion or low-flow perfusion) on mitochondrial function in the cells in vivo. Skinned fibers were obtained by using saponin for permeabilization of the sarcolemma in separated fiber bundles cut from left ventricle. The experimental protocol of the respiration rate determination included a cytochrome c test to check the intactness of the outer mitochondrial membrane. The apparent K(m) for ADP and the effect of creatine on the mitochondrial activity were also evaluated in these permeabilized fibers, taken from different groups of hearts. The preservation of low-flow perfused hearts resulted only in a slight decrease of creatine (20 mM) stimulated respiration at 0.1 mM ADP. The fibers from ischemic hearts or from hearts preserved by immersion showed a decrease of the apparent K(m) for ADP, and a complete loss of the stimulatory effect of creatine. In these fibers, we could observe that the outer mitochondrial membrane was damaged. In conclusion, the results of this study show that assessment of mitochondrial parameters sensitive to organelles swelling--intactness of outer membrane and functionally coupled creatine kinase reaction--are the most sensitive indicators of early hypoxic or ischemic damage to mitochondria. Their determination in biopsy samples could be used for evaluation of the efficiency of the cardiac protection in heart surgery.

The effects of halothane and isoflurane on the phosphoenergetic state of the liver during hemorrhagic shock in rats: an in vivo 31P nuclear magnetic resonance spectroscopic study

We studied the effects of halothane versus isoflurane on the phosphoenergetic state and intracellular pH (pHi) of the rat liver using in vivo 31P nuclear magnetic resonance (NMR) spectroscopy during and after hemorrhagic shock. Seventeen rats were anesthetized with 1 minimum alveolar anesthetic concentration of halothane or isoflurane. The mean arterial blood pressure was reduced to 40 mm Hg and maintained at this level for 45 min by withdrawing blood from the common carotid artery. The shed blood was then returned slowly. In vivo 31P NMR spectra were consecutively collected throughout the study. The phosphoenergetic state of the liver was evaluated from the changes in adenosine triphosphate (ATP) and inorganic phosphate (P(i)) levels. pHi was calculated from the chemical shifts of P(i) and alpha-ATP peaks. During hemorrhagic shock, beta-ATP decreased to 35% and 45%, and P(i) increased to 300% and 230% of their initial values in the halothane and isoflurane groups, respectively. Intracellular acidosis was more severe in the halothane group. The recoveries of beta-ATP and P(i) were better in the isoflurane group. Halothane showed a more detrimental effect than isoflurane on the hepatic phosphoenergetic level during and after hemorrhagic shock.

Inhibition of P-glycoprotein ATPase activity by beryllium fluoride

ATPase activity of P-glycoprotein (multidrug-resistance protein) was found to be potently inhibited by beryllium fluoride (BeFx) in combination with MgATP, MgADP, or corresponding Mg-8-azido-nucleotides. Inhibition was due to trapping of nucleoside diphosphate at catalytic sites. Full inhibition was achieved on trapping of 1 mol of nucleotide per mol of Pgp. Reactivation was slow (t(1/2) = 32 min at 37 degrees C), and release of trapped nucleotide correlated with recovery of ATPase. Trapping of 8-azido-ADP followed by UV irradiation yielded permanent inactivation and specific labeling of Pgp in plasma membranes. Both N- and C-terminal nucleotide binding sites were labeled. These findings give strong confirmation of the concepts that in intact Pgp both nucleotide sites are active in MgATP hydrolysis, and that they interact strongly. The characteristics of inhibition by BeFx were similar in general to those seen with vanadate. However, PPi gave strong protection against BeFx inhibition, and in this respect, inhibition by BeFx was clearly different from vanadate inhibition.

Oxidative energy metabolism in equine tendon cells

Hypoxia has been suggested as a possible cause of tissue degeneration and subsequent rupture in equine tendons. To determine whether low oxygen tension is likely to be detrimental to tendon cell function, experiments were designed to investigate oxidative energy metabolism in freshly isolated and cultured equine tendon cells. Freshly isolated tenocytes and cultured fibroblasts possessed activities of the mitochondrial enzyme citrate synthase similar to those of other mammalian cells, with well defined oxidative metabolism. D-[6(-14)C]-glucose oxidation was measurable in both freshly isolated and explant-derived cells. The content of adenosine triphosphate (ATP) in cultured cells was decreased by incubation with a mitochondrial respiratory uncoupler. These data demonstrate that tendon cells are capable of oxidative energy metabolism and rely upon it to maintain cellular ATP levels. Hypoxia must therefore be considered as a possible factor leading to tendon degeneration and subsequent injury.

Analysis of individual purine and pyrimidine nucleoside di- and triphosphates and other cellular metabolites in PCA extracts by using multinuclear high resolution NMR spectroscopy

This work demonstrates that individual purine and pyrimidine NDP and NTP can be assigned in high resolution 31P NMR spectra from tissue extracts. To the best of our knowledge, it is shown for the first time that ATP, GTP, UTP, CTP, and the corresponding diphosphates can be quantitated in cell extracts without using HPLC or other biochemical methods. This work provides the basis for further optimization of nucleotide quantitation by 31P NMR spectroscopy, and for a full assessment of this method. Furthermore, a new technique was developed for 1H, 31P, and 13C NMR signal assignment and quantitation in cell extracts by using the same external reference capillary for all three nuclei. This allows for efficient, quantitative, multinuclear NMR spectroscopy without extract contamination by standard material.

Regional deficits of myocardial blood flow and function in left ventricular pacing-induced heart failure

BACKGROUND

Pacing-induced congestive hear, failure has become a preferred model for the study of the pathogenesis of dilated cardiomyopathy. However, little is known regarding regional myocardial blood flow and function during the development of heart failure in this model.

METHODS AND RESULTS

To determine whether regional differences in myocardial blood flow are associated with regional dysfunction in ventricular pacing-induced heart failure, regional myocardial blood flow (radioactive microspheres) and regional wall thickening (transthoracic echocardiography) were measured in pigs studied at weekly intervals during the progression of heart failure induced by rapid pacing from the lateral wall of the left ventricle (220 +/- 9 bpm for 26 +/- 4 days). Echocardiography and hemodynamic measurements with the pacemaker off showed progressive, severe global left ventricular dysfunction. During pacing over the 3- to 4-week period, a progressive decrease in systolic wall thickening in the lateral wall occurred compared with the interventricular septum (IVS; P = .001); at 21 to 28 days, the difference was 50% (lateral wall, 14 +/- 6%; IVS, 28 +/- 6%; P = .0001). A difference in subendocardial blood flow per beat between the left ventricular lateral wall (the site of stimulation) and the IVS was found immediately on the initiation of pacing (IVS, 0.009 +/- 0.002 mL.min-1.g-1.beat-1; lateral wall, 0.005 +/- 0.001 mL.min-1.g-1.beat-1; P = .001), a difference that was sustained during pacing throughout the study. Subendocardial blood flow per beat was normal in both regions with the pacemaker off throughout the study.

CONCLUSIONS

These data indicate that regional myocardial ischemia is associated with the development of contractile dysfunction of the paced wall during prolonged rapid left ventricular pacing and that regional stunning contributes to persistent global left ventricular dysfunction when pacing is discontinued.

31P-magnetic resonance spectroscopy studies of nucleated and non-nucleated erythrocytes; time domain data analysis (VARPRO) incorporating prior knowledge can give information on the binding of ADP

Human erythrocytes have no nucleus, mitochondria or endoplasmic reticulum, whereas chicken erythrocytes have a nucleus and mitochondria and are closer in internal morphology, to cells such as the hepatocyte. Erythrocytes were used to test the hypothesis that 31P-MRS invisibility of ADP is associated with the presence of intracellular organelles. Simple frequency domain spectral analysis methods showed that all the acid extractable ADP (and ATP) was MR-visible in human erythrocytes. However, such methods gave variable estimates for 31P-NMR spectra of fresh chicken erythrocytes from which no conclusions could be drawn about the MR-visibility of ADP. Only when the data were fitted by a method incorporating prior knowledge of the ATP and ADP peak structure, using the time domain VARPRO method, was it possible to conclude that in fresh chicken erythrocytes, similar to other nucleated cells (liver, muscle), all the acid extractable ADP appeared to be MRS invisible, indicating binding or sequestration by intracellular organelles.

Characterisation of secondary metabolites associated with neutrophil apoptosis

We studied changes in secondary metabolites in human neutrophils undergoing constitutive or tumour necrosis factor (TNFalpha) stimulated apoptosis by a combination of high-performance liquid chromatography (HPLC) and NMR spectroscopy. Our results show that in contrast to freshly isolated neutrophils, neutrophil cells aged for 20 h in vitro had marked differences in the levels of a number of endogenous metabolites including lactate, amino acids and phosphocholine (PCho). There was no change in the concentration of taurine or glutamate and the ATP/ADP ratio was not affected. Levels of glutamine and lactate actually decreased. Identical changes were also observed in neutrophils stimulated to undergo apoptosis over a shorter time period (6 h) in the presence of TNFalpha and the phosphatidylinositol-3-kinase inhibitor wortmannin (WM). The changes in the concentration of PCho suggest possible activation of phospholipase associated with apoptosis or a selective failure of phosphatidycholine synthesis. The increased levels of apoptosis obtained with WM+TNFalpha, compared to TNFalpha by itself, suggest a synergistic effect by these compounds. The acceleration in rate of apoptosis probably arises from suppression by WM of pathway(s) that normally delay the onset of apoptosis. Changes in PCho and other endogenous metabolites, if proven to be characteristic of apoptosis in other cell systems, may permit non-invasive quantification of apoptosis. '

Prolonged adverse effects of benzalkonium chloride and sodium dodecyl sulfate in a primary culture system of rabbit corneal epithelial cells

This investigation was undertaken to determine prolonged adverse effects of benzalkonium chloride (BzCl), a cationic surfactant, and sodium dodecyl sulfate (SDS), an anionic surfactant, after an initial treatment of and subsequent removal from a primary culture system of rabbit corneal epithelial cells. Metabolic integrity and cell growth were evaluated at specified periods after a 1-hr treatment with the surfactants because of their importance in tissue repair. Intracellular calcium ([Ca2+]i) and intracellular pH (pHi) were also measured because of their importance in cellular homeostasis. ATP/ADP ratios were used to assess metabolic integrity, and propidium iodide staining of cells was used to measure relative cell number and cell growth. Digitized fluorescence imaging was used to measure [Ca2+]i with fura-PE3 and pHi with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). BzCl induced a concentration-dependent decrease in ATP/ADP ratios 24 hr after its removal from the cultures, whereas SDS had minimal effects on metabolic integrity throughout the 48-hr postexposure measurement period. The proliferative response of cultures treated with SDS, however, was decreased when compared with BzCl-treated cells. BzCl induced an increase in [Ca2+]i, whereas SDS decreased [Ca2+]i 1-3 hr after removal of surfactants. BzCl produced a sustained decrease in pHi in surviving cells 1-4 hr after its removal, with a return to control values at 24-48 hr. SDS transiently increased pHi 1 hr after its removal and decreased pHi at the 48-hr post-treatment period. In conclusion, the two surfactants in vitro had distinctly different prolonged effects on corneal epithelial cells, which may suggest that BzCl and SDS differentially affect cellular recovery in vivo.

The bound adenine nucleotides of purified bovine mitochondrial ATP synthase

The experiments in this study were directed towards defining the nucleotide content of purified beef-heart mitochondrial F1F0 ATP synthase during binding and hydrolysis of ATP. The purified, soluble synthase as prepared contained 2 mol ATP and 2 mol ADP/mol enzyme. Three of these four nucleotides were exchangeable on incubation with radiolabelled MgATP. Passage of the ATP synthase through a column of Sephadex G-50 readily removed 1 mol ADP/mol. The remaining bound nucleotides were not displaced by incubation with 1 mM GTP or 5 mM sodium sulfite, the latter an activator of the ATPase activity of the synthase. Incubation of the synthase with 250 microM MgATP in the presence of 3 mM sodium azide, an inhibitor of the ATPase, resulted in the transitory formation of a form of the enzyme in which 5-6 nucleotide-binding sites were loaded with ATP and/or ADP, thus showing that the ATP synthase, like the soluble F1 ATPase, contained a minimum of six nucleotide-binding sites. The presence of an ATP-regenerating system during incubation with MgATP resulted in the loading of 5-6 sites to yield a form of the enzyme containing 3-4 mol ATP and 2 mol ADP/mol synthase even after passage through a centrifuged column. Following hydrolysis of the medium MgATP, the enzyme reached a stable form containing 2 mol ATP and 2 mol ADP/mol synthase. Like the form of the enzyme originally prepared, 1 mol ADP/mol synthase was readily released. However, this ADP remained bound to the synthase in the presence of GTP if azide was present. These results are discussed in the context of current ideas about nucleotide-binding sites on the F1 ATPase portion of the F1F0 ATP synthase. It is concluded that the properties of the sites on the F1F0 synthase show some differences from those on the F1 ATPase.

Effect of nucleotides, peptides, and unfolded proteins on the self-association of the molecular chaperone HSC70

In a previous study, we showed that the molecular chaperone HSC70 self-associates in solution in a reversible and likely unlimited fashion. Here, we examine the influence of nucleotides, nucleotide analogs, peptides, and unfolded proteins on the self-association properties of this protein. Whereas in the presence of ADP, HSC70 exists as a slow, concentration- and temperature-dependent monomer-oligomer equilibrium, in the presence of ATP, the protein is essentially monomeric, indicating that ATP shifts this equilibrium toward the monomer by stabilizing the monomer. Dissociation of oligomers into monomers is also obtained with the slowly hydrolyzable ATP analogs, adenosine 5'-O-(thiotriphosphate) and 5'-adenylyl-beta,gamma-imidodiphosphate, or the complex between ADP and the phosphate analog, BeF3, indicating that binding but not hydrolysis of ATP is necessary and sufficient for the stabilization of HSC70 monomer. Furthermore, binding of short peptides or permanently unfolded proteins to the peptide binding site of HSC70 promotes the dissociation of oligomers into monomers, suggesting that protein substrates are able to compete with HSC70 for the same binding site. Because the release of peptides or unfolded proteins from HSC70 has also been shown to require ATP binding, these results indicate that dissociation of oligomers is controlled by a mechanism similar to that of release of protein substrates and suggest that binding of HSC70 to itself occurs via the peptide binding site and mimics binding of HSC70 to protein substrates.

31P NMR methods for the direct determination of ADP in the presence of ATP

A new method is presented for the direct measurement of the amount of ADP in the presence of ATP by selectively eliminating the alpha- and gamma-ATP signals. The method is compared with other methods, both experimentally and theoretically, using the product-operator formalism. An analysis of the effect of beta 1 inhomogeneity on the efficiency of the methods is also given. Experimental results obtained using adiabatic pulses to compensate for such effects are shown. The accuracy of this new method is demonstrated by measuring various ADP concentrations in a series of solutions containing ADP and ATP.

Agonist-free transformation of the glucocorticoid receptor in human B-lymphoma cells

Nuclear translocation of activated glucocorticoid receptors (GRs) is a necessary step in the signal transduction by these GC hormones. Although in vitro activation of GRs can occur in the absence of a functional ligand, it is generally assumed that binding of a cognate hormone is required for activation of the intracellular GR. By indirect immunocytochemistry and Western-blot analysis, it was found that, in spontaneously aggregated human lymphoma DoHH2 cells, hormone-free GRs are located in the nucleus. Disruption of the aggregates redistributed GRs to a predominantly cytosolic location. Upon spontaneous re-aggregation the GR again became localized to the nucleus. Intracellular cross-linking of the heteromeric receptor complex was applied to investigate the protein composition of cytoplasmic and nuclear receptors. Untransformed, cytosolic GRs could be demonstrated by [3H]dexamethasone binding capacity and hsp90 co-immunoprecipitation, whereas absence of these characteristics suggested an activated conformation of the nuclear GRs. These observations suggest that cell-cell interactions are capable of transforming GRs in the absence of a ligand.

Modelization of coordinated changes of adenylate energy charge and ATP/ADP ratio: application to energy metabolism in invertebrate and vertebrate skeletal muscle

Regulation of the coordinated adenylate energy charge (AEC) and ATP/ADP ratio variations was studied with the aid of computer-made simulations. When the equilibrium state for the adenylate kinase-catalyzed reaction has been assumed, the function describing the coordinated AEC and ATP/ADP ratio variations can be simply derived from the formulas describing these 2 parameters. The model was used to analyze incidence of AMP deamination in the coordinated regulation of cellular energy metabolism.